Mycobacterium leprae and Mycobacterium tuberculosis are the causative agents of leprosy and tuberculosis respectively. Control of these diseases is a serious health problem in the underdeveloped and developing countries. Resurgence of tuberculosis in the developed nations has also been a serious concern in the recent past. Several immunodominant proteins of these bacteria have been identified in order to study the pathogenesis of these diseases, and to understand the response of these bacteria to the human immune system. Among these antigens, those with molecular weights of around 10kD have been shown to be the most potent stimulators of the immune system. These cross react with substantial population of the reactive T-cells We are undertaking work to determine crystal structures of these proteins.